The present invention relates to methods for improving production from subterranean formations. More particularly, the present invention relates to methods for improving the permeability of particulates placed in subterranean formations.
Subterranean operations often use particulates, such as proppant and gravel, substantially coated with a tackifying agent, e.g., a material that exhibits a sticky or tacky character. As used herein, the term “tacky,” in all of its forms, generally refers to a substance having a nature such that it is somewhat sticky to the touch. These particulates that have been substantially coated with a tackifying agent will be referred to herein as “tackified particulates.”
One example of a production stimulation operation using such tackified particulates is hydraulic fracturing, wherein a formation is treated to increase its conductivity by hydraulically fracturing the formation to create or enhance one or more cracks or “fractures.” In most cases, a hydraulic fracturing treatment involves pumping a proppant-free, viscous fluid (known as a pad fluid) into a subterranean formation faster than the fluid can escape into the formation so that the pressure in the formation rises and the formation breaks, creating a new fracture or enlarging a natural fracture. Once the fracture is formed or enlarged, proppant particulates are generally placed into the fracture to form a proppant pack that may prevent the fracture from closing when the hydraulic pressure is released. A portion of the proppant particulates may be coated with a tackifying agent, among other things, to control formation fines from migrating into the proppant pack.
An example of a well completion operation using a treating fluid containing tackified particulates is gravel packing. Gravel packing treatments are used, among other things, to reduce the migration of unconsolidated formation sands into the well bore. Typically, gravel packing operations involve introducing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel particulates designed to prevent the passage of formation sands through the pack. In some instances, the gravel particulates may comprise tackified particulates. The gravel pack screen is generally a type of filter assembly used to support and retain the gravel placed during the gravel packing operation. A wide range of sizes and screen configurations are available to suit the characteristics of a particular well bore, the production fluid, and the formation sands. When installing the gravel pack, the gravel particulates are suspended in a treatment fluid, which may be viscosified, and the treatment fluid is pumped into a well bore in which the gravel pack is to be placed. Once the gravel particulates are placed in the well bore, the viscosity of the treatment fluid is reduced, and it is returned to the surface. The resultant gravel pack may be used to stabilize the formation while causing minimal impairment to well productivity, for example, by preventing formation sands from occluding the screen or migrating with the produced fluids and/or preventing the gravel particulates from entering the well bore.
In some situations, the processes of hydraulic fracturing and gravel packing are combined into a single treatment to stimulate production and reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, these treatments are completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the hydraulic fracturing treatment usually ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation.
Operations using tackified particulates often lose their usefulness over time as unconsolidated or weakly consolidated formation fines within the formation migrate with fluids within the formation and attach to the surface of the tackified particulates by sticking to the tackifying agent coated on the particulates. As used herein, the term “formation fine(s)” refers to any loose particles within the portion of the formation, including, but not limited to, formation fines, formation sand, clay particulates, coal fines, resin particulates, unconsolidated proppant or gravel particulates, portions of unconsolidated proppant or gravel particulates, and the like. While such attachment may be desirable in that it may help control the formation fines from moving beyond the tackified particulates, the attachment of formation fines essentially acts as a partitioning agent that is applied over time. Eventually, the formation fines attached to the tackified particulates may plug the formation-particulate interface and even invade further into the proppant or gravel pack. This may cause the well's production to fall off quickly.